Human cells produce reactive oxygen species when infected by a bacterial pathogen. This oxidative burst is intended to kill the would-be invader. Several bacterial transcription factors have been characterized that respond to reactive oxygen species to control gene expression and mount a defense against this oxidative burst. It has also been shown that an inefficient bacterial response to host-derived reactive oxygen species reduces infectivity. It is therefore of importance to human health to understand the full spectrum of host-pathogen interactions to be able to administer effective antimicrobial agents. In this program, we focus on a related aspect of the oxidative burst, namely the concomitant production of urate. Urate is produced because one of the two main enzymes responsible for production of reactive oxygen species is xanthine oxidase, which functions in purine degradation to convert hypoxanthine to xanthine and xanthine to urate. Based on our previous work in which we demonstrated that urate functions as a ligand for a transcription factor encoded by plant pathogens to mediate gene regulation, we now focus on two specific hypotheses: 1-That urate functions as a signaling molecule to effect gene regulation in certain bacterial species that are important human pathogens, and 2- that urate-mediated gene regulation is effected by a subset of transcriptional regulators that belong to the Multiple Antibiotic Resistance Regulator (MarR) family. Using Burkholderia thailandensis as a model system, we plan to identify the mechanism of urate-mediated attenuation of DNA binding by this transcription factor as well as the regulon under its control, and we plan to determine the role of urate-dependent transcriptional regulation in response to oxidative stress. The proposed experimental plan will extend the known mechanisms by which gene expression is regulated in response to oxidative stress with the associated potential for a deeper understanding of host-pathogen interactions, and it will furnish an environment in which students will be exposed to biomedical research.